EP1632084B1 - Impedance adapter for a high-bandwidth transmission channel of a copper-wired terminal system - Google Patents

Abstract

Device has an adjustment module (10) constituted by a RC circuit to insert a termination impedance in a connection plug (P), when the plug is not connected to a high rate VDSL (Very high bit-rate Digital Subscriber Line) type modem. Coupling module (20) couples with the adjustment module when the modem is connected to the plug, to transform the inserted impedance such that the plug is transparent to high rate transmission of broad band services. An independent claim is also included for a copper terminal installation with an impedance matching device.

Description

The present invention relates to an impedance adapter device of the high-speed transmission channel of a copper terminal installation.

The invention lies in the field of broadband transmissions and typically finds application in the transmission of broadband services delivered to an ITC copper terminal installation connected to an access network.

In the current context of increasing transmission speeds and the explosion of Internet services, many broadband access systems have been introduced to subscribers. These high-speed access systems use existing wiring, that is twisted copper pair wiring. Thus, digital coding x-DSL type can transport on the existing copper pairs of the analog telephone network (RTC) or digital (ISDN) high speeds ensuring towards users of fast Internet type services. or visual audio. X-DSL denotes all broadband broadband services including all technology families such as HDSL, SDSL, ADSL, VDSL, ADSL-Lite etc ...

However, these x-DSL systems, which make it possible to convey voice and data on the same medium, must be able to adapt to the different topologies of the copper terminal infrastructure (end-of-line sections, bridge or shunt, their length etc ...), support all the dynamic variations of the transmission characteristics and coexist with narrow-band voiceband services (analogue or ISDN).

This requirement applies essentially for systems operating at very high frequency, typically in a spectral band greater than 3 MHz. This is the case, for example, of VDSL systems whose frequency spectrum is very wide since it ranges from 138 kHz to 12 MHz. Indeed, the use of a transmission channel in a high frequency range is not without consequences on the quality of the link. Transmission in the spectral band above 3 MHz, in particular, is sensitive to reflections on the line due to the existence of open branches and / or capacitive loads.

An open branch is defined as any unconnected line end section, ie any unoccupied telephone connection socket. Capacitive load defines any line end section connected to a capacitive load narrowband terminal, for example a telephone set, via a telephone jack.

In the context of international standardization, two VDSL frequency plans, called 997 and 998, and incompatible spectra were included in the ETSI standard. The former offers greater room for the upstream channel and favors symmetrical broadband speeds (26 Mbit / s in the downstream direction and 26 Mbit / s maximum in the upstream direction), while the second favors asymmetric throughput with a higher frequency. higher throughput on the downstream channel (34 Mbps on the downstream channel and 4 Mbps on the upstream channel).

• la figure 1 est un schéma d'une installation terminale cuivre selon l'état de la technique comprenant un filtre unique,
• la figure 2 est un schéma d'une installation terminale cuivre selon l'art antérieur comprenant des filtres distribués.

The invention will now be presented with regard to the prior art:

• the figure 1 is a diagram of a copper terminal installation according to the state of the art comprising a single filter,
• the figure 2 is a diagram of a copper terminal installation according to the prior art including distributed filters.

A terminal copper installation (ITC) can have two types of possible configurations. It can indeed present a so-called "private" configuration, of suburban type, or a so-called "collective" configuration, of the service type of building. The present invention applies equally to both types of configuration.

A conventional VDSL link comprises two pieces of equipment: a multi-port DSL access multiplexer, still classically noted DSLAM, and a user modem respectively located at the central office and at the user's premises within a copper terminal installation (ITC) and connected between them through an RA access network. The maximum length of the line is about 1 km. In the case of an architecture called "FTTCab", the DSLAM is deported from the central office to a sub-distributor and the connection between the central office and the DSLAM is fiber optic. These architectures are known to those skilled in the art and are not more detailed here.

The VDSL link must also be transparent to the voice phone. In the user, the point of entry of the copper terminal installation (ITC) is made from the home entry strip, also called NID (Network Interface Device), and the function filtering, to separate the voice band from the broadband services, can be performed according to the two cases of installation shown on the Figures 1 and 2 .

In the first case ( figure 1 The ITC includes a device, commonly referred to as a "splitter", comprising a single FU filter at the home entrance, just behind the NID. This unique filter FU filters the low end of the spectrum. Thus, the "splitter" makes it possible to separate the voiceband, which is directed to narrowband terminals TBE1, TBE2 such as telephones, broadband services, which are transmitted to a broadband terminal TBL, such as a computer for example, via a broadband modem M of VDSL type in this particular example. This type of FU filter is generally a high order filter (n> 5) which requires the intervention of the telephone operator for his installation at the user.

In the second case ( figure 2 ) the ITC includes distributed filters FD1, FD2. These filters are passive micro-filters, generally of order 2, which can be plugged into the telephone connection sockets, in front of the narrowband terminals TBE1, TBE2. These filters thus make it possible to prevent broadband signals from disrupting telephony and vice versa. They are low cost components and easy to implement by the user himself. However, we can not multiply indefinitely their number because the resulting impedance that they present can then be penalizing for the values of losses by reflection, more commonly called "return-loss", and which can consequently degrade the quality voice of the telephone link. Moreover, in the case of an ITC with distributed filters, the high-speed transmission in the 3-12 MHz frequency band is sensitive to reflections on the line in the presence of open branches BO1, BO2 and / or capacitive loads TBE1 , TBE2.

To avoid this problem, one could insert into each socket termination impedance that would promote broadband transmission while reducing attenuation phenomena due to mismatch of the telephone line. Such a termination impedance would then preferably have a value close to the average value of the impedance of the copper cable of the telephone line, in the band of frequency between 3 and 12 MHz, that is to say a value of the order of 135 Ω. However, when a modem, of the VDSL type for example, is connected to such a telephone connection socket, in which a termination impedance has been previously inserted, the performance of the broadband link is degraded. Indeed, the socket connection is not transparent to the transmission of broadband services since the value of the impedance that was previously inserted is close to that of the modem (of the order of 135Ω in the band 3-12 MHz).

A solution to avoid the problems of degradation of the quality of the high-speed link in the 3-12 MHz frequency band due to mismatching of the line would be to adapt the open branches by inserting a termination impedance into the connection sockets. telephone, and remove said impedance previously inserted into a socket as soon as a modem is connected to this socket, in order to avoid degradation of the performance of the broadband link. However, this solution is very restrictive because it is completely manual and requires the user to think about removing the impedance previously inserted into a socket when he wants to connect a broadband modem.

The document of the prior art GB 2339506 describes a module that adapts the subscriber's telephone line by having a high impedance in the high frequency domain reserved for data communications.

Also, the technical problem of the present invention consists in proposing an impedance matching device of at least one high-speed transmission channel of a copper terminal installation connected to an access network delivering narrowband services (analog or ISDN) and broadband services (x-DSL), said installation comprising at least one broadband modem of x-DSL type, and at least one connection socket, which would make it possible to automatically adapt the impedance of the channel of high-speed transmission, depending on whether or not a modem is connected to a connection socket of the installation, on the one hand to avoid mismatches of the line due to the presence of open branches and / or capacitive loads, and on the other hand to avoid the problems of degradation of the performance of the broadband link, when a modem high-speed is connected to a connection socket in which a termination impedance has been inserted beforehand.

• un module d'ajustement, implanté dans ladite prise de raccordement, constitué par un circuit RC comprenant, en série, au moins une résistance (R), des condensateurs (C1, C2) et au moins une diode varicap (D1, D2), et destiné à insérer une impédance de terminaison dans ladite prise de raccordement, lorsqu'elle n'est pas connectée audit modem haut-débit,
• un module de couplage, raccordé au modem haut-débit (M) et destiné à s'unir audit module d'ajustement lorsque ledit modem haut-débit est raccordé à ladite prise de raccordement, comprenant des résistances (R1, R2), chacune d'elles étant destinée à être connectée en parallèle sur un condensateur (C1, C2) du module d'ajustement (10) de manière à polariser en inverse au moins l'une des diodes varicap (D1, D2), de manière à transformer l'impédance insérée dans la prise de raccordement de telle sorte que cette dernière devienne transparente à la transmission haut-débit de services large bande.

The solution to the technical problem raised is obtained, according to the present invention, by the fact that the adapter device comprises:

• an adjustment module, implanted in said connection socket, constituted by an RC circuit comprising, in series, at least one resistor (R), capacitors (C1, C2) and at least one varicap diode (D1, D2), and for inserting a termination impedance into said socket, when not connected to said broadband modem,
• a coupling module, connected to the high-speed modem (M) and intended to unite with said adjustment module when said high-speed modem is connected to said connection socket, comprising resistors (R1, R2), each of they being intended to be connected in parallel on a capacitor (C1, C2) of the adjustment module (10) so as to reverse bias at least one of the varicap diodes (D1, D2), so as to transform the impedance inserted in the socket so that it becomes transparent to broadband broadband transmission.

Thus, the adjustment module makes it possible to insert a termination impedance, of finite value, into the connection socket. It thus serves as a stopper and protects the high-speed connection against reflections on the line, that is to say the mismatches due to the presence open branches and / or capacitive loads, which strongly disturb the high-speed transmission in the frequency band between 3 and 12 MHz. In addition, when the broadband modem is connected to a connection socket, the adjustment module and the coupling module unite to automatically change the impedance of the tap, in the frequency band 3-12. MHz, so that the resulting impedance is infinitely large. This resulting impedance then for example has a value between 1 kΩ and 10 MΩ, and becomes transparent vis-à-vis the high-speed transmission.

The invention further relates to a copper terminal installation connected to an access network carrying narrowband services and broadband services and comprising connection jacks and at least one high-speed x-DSL modem. This installation is remarkable in that it comprises impedance adapter devices according to the invention.

• Une étape d'ajustement comportant l'insertion d'une impédance de terminaison dans ladite prise (P ; P1, P2, P3) de raccordement, pour insérer un module d'ajustement (10, 30) comprenant, en série, au moins une résistance (R), des condensateurs (C1, C2) et au moins une diode varicap (D1, D2), lorsqu'elle n'est pas connectée audit modem haut-débit (M),
• et, lorsque ledit modem haut-débit est raccordé à ladite prise de raccordement, une étape de couplage comportant la transformation de ladite impédance insérée dans la prise de raccordement, de telle sorte que cette dernière devienne transparente à la transmission haut-débit de services large bande, pour insérer un module de couplage (20, 40) comprenant des résistances (R1, R2), chacune d'elles étant destinée à être connectée en parallèle sur un condensateur (C1, C2) dudit module d'ajustement (10) de manière à polariser en inverse au moins l'une des diodes varicap (D1, D2).
  Dans toute la suite de la description, il est fait référence à une liaison haut-débit de type VDSL, mais bien sûr l'invention ne se limite pas à ce type d'application. Elle s'applique en fait à toute liaison haut-débit dont le spectre fréquentiel est supérieur à 3 MHz.
  D'autres particularités et avantages de l'invention apparaîtront à la lecture de la description suivante faite à titre d'exemple illustratif et non limitatif, en référence aux figures annexées, qui représentent .
• la figure 1, déjà décrite, un schéma d'une installation terminale cuivre selon l'état de la technique comprenant un filtre unique,
• la figure 2, déjà décrite, un schéma d'une installation terminale cuivre selon l'état de la technique comprenant des filtres distribués,
• la figure 3, un schéma d'un dispositif selon l'invention,
• la figure 4, un schéma du dispositif de la figure 3 selon une configuration dissociée,
• la figure 5, un schéma du dispositif de la figure 3 selon une configuration assemblée,
• la figure 6, un schéma d'un dispositif selon un deuxième mode de réalisation et selon une configuration assemblée,
• la figure 7, un schéma d'une installation privative dans laquelle des mesures de débit en ligne ont été effectuées en présence et en l'absence du dispositif de la figure 3.

The invention also relates to a method of impedance matching of at least one high-speed transmission channel of a copper terminal facility (ITC) connected to an access network providing narrow-band services and broadband services. , said installation comprising at least one high-speed modem (M), and at least one connection socket (P; P1, P2, P3), characterized in that the method comprises the following steps:

• An adjustment step comprising inserting a termination impedance into said connection socket (P; P1, P2, P3) to insert an adjustment module (10, 30) comprising, in series, at least one resistor (R), capacitors (C1, C2) and at least one varicap diode (D1, D2), when not connected to said high-speed modem (M),
• and, when said broadband modem is connected to said socket, a coupling step includes transforming said impedance inserted in the socket, so that the socket becomes transparent to broadband broadband transmission. strip, for inserting a coupling module (20, 40) comprising resistors (R1, R2), each of them being intended to be connected in parallel on a capacitor (C1, C2) of said adjustment module (10) so as to reverse bias at least one of the varicap diodes (D1, D2).
  Throughout the remainder of the description, reference is made to a high-speed link of the VDSL type, but of course the invention is not limited to this type of application. It applies in fact to any broadband link whose frequency spectrum is greater than 3 MHz.
  Other features and advantages of the invention will appear on reading the following description given by way of illustrative and non-limiting example, with reference to the appended figures, which represent.
• the figure 1 , already described, a diagram of a copper terminal installation according to the state of the art comprising a single filter,
• the figure 2 , already described, a diagram of a copper terminal installation according to the state of the art including distributed filters,
• the figure 3 , a diagram of a device according to the invention,
• the figure 4 , a diagram of the device of the figure 3 according to a dissociated configuration,
• the figure 5 , a diagram of the device of the figure 3 according to an assembled configuration,
• the figure 6 a diagram of a device according to a second embodiment and according to an assembled configuration,
• the figure 7 , a diagram of a private installation in which online flow measurements were made in the presence and in the absence of the device of the figure 3 .

The figure 3 schematizes an impedance matching device of at least one high-speed transmission channel of a copper terminal installation. This device, referenced 100, comprises two distinct modules, referenced 10 and 20, which make it possible to automatically insert a different impedance value into the connection socket P, at the input of the access network, depending on whether a high-level modem flow M is connected or not to this connection socket P.

The LT line, whose voltage supply is typically -48 V, carries both narrow band and broadband services.

The first module, referenced 10, is an adjustment module which is located in the connection socket P. This module makes it possible to insert a termination impedance of finite value into the socket P.

The second module, referenced 20, is a coupling module which is preferably connected to the broadband modem, for example attached to the modem connection socket. This module is intended to unite with the adjustment module 10 at the time of connection of the modem to the socket P. This union of the two modules makes it possible to automatically modify the value of the impedance inserted in the connection socket P so that it can become transparent to high-speed transmission in the frequency band between 3 and 12 MHz.

The adapter device comprises passive components that are inexpensive and compact. The small size of this device therefore allows to integrate it into the same housing 1000 as a distributed filter 200.

The distributed filter 200 makes it possible to mask the impedance of the narrowband terminal TBE whose capacitive load is detrimental to the quality of the broadband transmission channel. It conventionally comprises an LC circuit.

The impedance adapter device is connected to the connection socket P, preferably in parallel with the distributed filter 200 which is housed in the same housing 1000.

The fact of introducing a termination impedance into the telephone connection socket P makes it possible to avoid the impedance variations that may occur on the telephone line LT, in the band 3-12 MHz, due to the presence of branches. open and / or capacitive loads in the private facility.

The adjustment module 10, as illustrated on the figure 4 , allows to introduce this termination impedance into the socket P.

For this, the module is in the form of an RC circuit. More precisely, this circuit comprises at least one resistor R, capacitors C1, C2 and diodes with variable capacitance D1, D2, also called varicap or varactor diodes. All these components are connected in series.

Varicap diodes are known to have a capacitance that varies when reverse biased. In fact, their capacity decreases when the reverse voltage increases. Thus, the diodes D1 and D2 have a capacitance which can vary from a few pF to some 100 pF depending on the applied voltage.

In the example shown on the figure 4 these diodes are two in number. However, it is conceivable to realize this type of device with more than two varicap diodes, provided that their number is even.

Finally, these diodes are arranged head to tail in order to reverse bias one of the two diodes and this independently of the polarity of the telephone line, as is described in more detail below with respect to the figure 5 . These two diodes can be mounted indifferently anode against anode, or cathode against cathode. In the configuration shown in figure 4 , where the adapter device is dissociated and only the adjustment module is implanted in the connection socket, the diodes D1 and D2 are not reverse biased because they are isolated by the capacitors C1 and C2 arranged on either side .

In this case the entire device has an impedance equal to the value of the resistor R, and preferably of the order of 135 Ω in the frequency band 3-12 MHz, this impedance value corresponding to the average value. of the constituent cable the telephone line in this frequency band. To obtain this impedance, the values of the components are judiciously calculated and chosen. By way of example, the capacitors C1 and C2 each have a capacitance of 100 nF while the resistor R has a value of 135 Ω.

The figure 5 schematizes the impedance matching device in an assembled configuration, i.e., when the adjustment and coupling modules 20 are joined together. A high-speed modem M, on whose plug the coupling module 20 is inserted, is connected to the installation via a connection socket in which the adjustment module 10 has been inserted beforehand. Thus, when the modem is connected to the socket, the modules 10 and 20 are assembled and cooperate so as to automatically transform the impedance inserted in the socket so that it can become transparent to the high-speed transmission in the band of frequencies 3-12 MHz.

The coupling module comprises four contact points E1, S1; E2, S2; E3, S3; E4, S4. Two of them, E1, S1 and E4, S4 are used for connection to the modem M. The other two contacts E2, S2 and E3, S3 are recovered to bias the varicap diodes D1 and D2 of the adjustment module, through resistors R1 and R2.

Indeed, the fact of placing the resistor R1 in parallel on the capacitor C1 of the adjustment module and the resistor R2 in parallel on the capacitor C2 of the adjustment module, makes it possible to neutralize the capacitors C1 and C2 and to modify the voltage supplying the varicap diodes D1, D2 and polarizing at least one in reverse, from the supply voltage of -48 volts of the telephone line LT.

The diodes being placed head to tail, one of them will therefore have a very low junction capacity compared to each other. This low capacitance of junction of one of the two diodes, D1 or D2 according to the polarization, makes it possible to obtain an infinite impedance, typically of the order of 1 kΩ to 10 MΩ.

At least one of the two resistors R1 or R2 has a very high value, typically between 2 and 5 MΩ, for example of the order of 2.2 MΩ, so that the current consumption is infinitesimal and the resulting impedance of the device it is not changed as well. The two resistors R1 and R2 may be of equal value to make symmetrical mounting for example.

In the proposed embodiment, component values were calculated to address different mismatch problems in the 3-12 MHz band. The choice of varicap diodes is important because it determines the limit values of the variable impedance. The best capacity ratio is obtained with commercially available type BB132 diodes in a proportion of 1 to 30. Using 6 diodes for example, a capacitance of 450 pF (with bias voltage = 0) at 16.5 pF (with a bias voltage of -28 V), which gives respective cut-off frequencies at about 3 and 80 MHz.

Above 10 MHz, the impedance of the adapter device is limited by that of the distributed filter (s) placed in parallel within the ITC if it is not ( are not suitable for VDSL transmission.

The figure 6 illustrates a second embodiment of an impedance matching device of at least one high-speed transmission channel of a copper terminal installation. In this arrangement, the adjustment module, referenced 30, has only one varicap diode D1. When only this adjustment module is implanted in a socket connection, the diode D1 is not reverse biased since it is isolated by the capacitors C1 and C2 arranged on both sides. In this case, the adjustment module has an impedance equal to the value of the resistor R, and preferably of the order of 135 Ω in the 3 - 12 MHz frequency band, as explained above with reference to the figure 4 .

In this embodiment, the coupling module, referenced 40, intended to join the adjustment module 30 when a high-speed modem M is connected to the connection socket, has a slightly more complex construction than in the first embodiment. The coupling module 40 always has four contact points E1, S1; E2, S2; E3, S3; E4, S4; two of them E1, S1 and E4, S4 being used for the connection to the modem M. The two other contacts E2, S2 and E3, S3 are recovered to reverse bias the varicap diode D1 of the adjustment module by means of a bridge rectifier and a resistor bridge R3, R4. The rectifier bridge, disposed in the coupling module 40, is constituted by rectifying diodes D2, D3, D4, D5 mounted two by two in parallel and head to tail. The rectifier bridge integrated in the coupling module makes it possible to modify the supply voltage of the varicap diode D1 and reverse bias it from the supply voltage of -48 volts of the telephone line to obtain an infinite impedance. typically between 1 kΩ and 10 MΩ.

Preferably, the resistors R3 and R4 forming the resistor bridge have a high value, typically between 2 and 5 MΩ, for example of the order of 5 MΩ each, so that the power consumption is infinitesimal and that the resulting impedance of the device is not modified.

Tests were carried out on the impedance adapter device and focused on in-line flow measurements in both directions of transmission over a VDSL link. These tests made it possible to measure the impact of open branches and / or capacitive loads in the 3-12 MHz spectral band, with or without a device. This also made it possible to check the transparency of the latter vis-à-vis the broadband transmission.

The copper terminal installation in which these tests were carried out is represented on the figure 7 . The private facility starts at the NID home entry strip. The VDSL link includes a central-side equipment (DSLAM) with an integrated low-pass filter, 600m of cable and a VDSL modem M in the private part. The ITC comprises three P1, P2, P3 jacks connected to the access network in a star topology (6 m sections).

As shown in figure 7 , all the connection jacks P1 to P3 not only include distributed FD1 to FD3 filters distributed for the connection of TBE2 terminals in the voice band, but also DA1 to DA3 adapter devices for VDSL M modems or the open branches BO1 and / or capacitive TBE2. A VDSL modem M is connected to the third socket P3.

Inline flow measurements are provided by the proprietary system manager for a system noise margin of 6dB.

The table below summarizes the results obtained on a VDSL link with open branches adapted or not. Type of connection Online rate (Mbit / s) Downstream channel Upcoming channel Without an open branch 27.72 7.93 With unsuitable open branches 13.56 1.92 With adapted open branches 15.23 5.24

In the presence of noise E (standardized noise FFTExc on the central side and on the installation side), it is the upstream channel which is mainly affected and which therefore limits the performance of the VDSL link.

ITC mismatches (open branches, capacitive branches) and the topology of the ITC (star, bridge or bypass) must be taken into account as they add to the crosstalk noise present on the line.

The presence of termination impedances on open branches belonging to the Copper Terminal Facility (ITC) is desirable. The performance of a VDSL link of 600 m length with 2 open and / or capacitive branches 6 m long at the end of the line is degraded. In comparison, when inserting the adapter device at the end of each branch, the in-line flow rates in both directions of transmission are improved. This is especially true for the upward sense.

The impedance adapter device is also transparent to the broadband transmission.

By adapting the open branches to 135 Ω in the spectral band (3 - 12 MHz), the online rates on a VDSL link are significantly improved.

Finally, the impedance adapter device is made from low-cost components and can easily be integrated into the same housing as a distributed filter.

Claims (9)

1. Impedance adapter device for matching the impedance of at least one high-speed transmission channel of a copper terminal installation (CTI) hooked up to an access network delivering narrowband services, analogue or ISDN, and broadband services, x-DSL, said installation comprising at least one high-speed modem (M) of x-DSL type, and at least one jack (P; P1, P2, P3), characterized in that it comprises:

   - an adjustment module (10, 30), implanted in said jack (P; P1, P2, P3), consisting of an RC circuit comprising, in series, at least one resistor (R), capacitors (C1, C2) and at least one varicap diode (D1, D2), and intended to insert a terminating impedance into said jack (P; P1, P2, P3), when it is not connected to said high-speed modem (M),

   - a coupling module (20, 40), hooked up to the high-speed modem (M) and intended to be united with said adjustment module (10) when said high-speed modem (M) is hooked up to said jack (P; P1, P2, P3), comprising resistors (R1 ,R2), each of them being intended to be connected in parallel with a capacitor (C1, C2) of the adjustment module (10) so as to reverse bias at least one of the varicap diodes (D1, D2), so as to transform the impedance inserted into the jack in such a way that the latter becomes transparent to the high-speed transmission of broadband services.
2. Device according to Claim 1, characterized in that the adjustment module (10, 30) is disposed in parallel with a distributed filter (200).
3. Device according to Claim 1, characterized in that the adjustment module (10) comprises an even number of varicap diodes (D1, D2), disposed head-to-tail.
4. Device according to one of Claims 1 to 3, characterized in that the adjustment module (30) comprises a varicap diode (D1) and in that the coupling module (40) comprises a rectifier bridge, consisting of rectifying diodes (D2, D3, D4, D5), and a resistor bridge (R3, R4).
5. Device according to one of Claims 1 or 4, characterized in that one at least of the resistors (R1, R2; R3, R4) exhibits a value of between 2 and 5 MΩ.
6. Device according to any one of the preceding claims, characterized in that the high-speed modem (M) is a modem of the VDSL type.
7. Copper terminal installation (CTI), hooked up to an access network carrying narrowband services and broadband services, comprising jacks (P; P1, P2, P3) and at least one high-speed modem (M) of x-DSL type, characterized in that it comprises impedance adapter devices in accordance with one of Claims 1 to 6.
8. Installation according to Claim 7, characterized in that the adapter devices each exhibit two modules (10, 20; 30, 40) intended to be united when a high-speed modem (M) is connected to a jack (P; P1, P2, P3), the first module (10; 30) being implanted in said jack (P; P1, P2, P3) on the network access, and the other module (20; 40) being disposed in the jack socket of the high-speed modem (M).
9. Method of matching the impedance of at least one high-speed transmission channel of a copper terminal installation (CTI) hooked up to an access network delivering narrowband services and broadband services, said installation comprising at least one high-speed modem (M), and at least one jack (P; P1; P2, P3), characterized in that the method comprises the following steps:

   - an adjustment step comprising the insertion of a terminating impedance into said jack (P; P1, P2, P3), so as to insert an adjustment module (10, 30) comprising, in series, at least one resistor (R), capacitors (C1, C2) and at least one varicap diode (D1, D2), when it is not connected to said high-speed modem (M);

   - and, when said high-speed modem is hooked up to said jack, a coupling step comprising the transformation of said impedance inserted into the jack in such a way that the latter becomes transparent to the high-speed transmission of broadband services, so as to insert a coupling module (20, 40) comprising resistors (R1, R2), each of them being intended to be connected in parallel with a capacitor (C1, C2) of said adjustment module (10) so as to reverse bias at least one of the varicap diodes (D1, D2).

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